/Engine/Source/Runtime/Slate/Public/Framework/Docking/TabManager.h
Notify the tab manager that a tab has been relocated. If the tab now lives in a new window, the NewOwnerWindow should be a valid pointer.
void OnTabRelocated &40; const TSharedRef< SDockTab > & RelocatedTab, const TSharedPtr< SWindow > & NewOwnerWindow &41;